Means for sealing membrane carrying tubes

ABSTRACT

An osmotic membrane bridges over the joint between an end core fitting and the end of a tubular porous core member and alloys with the material of the core fitting. The joints may be between modules joined or coupled by male and female plastic core fittings linked together by bayonet joints. This assembly is adapted to use in reverse osmosis machines with the joined modules in a tubular shell forming an annulus with concentrate in the annulus under pressure. The bayonet joints prevent pulling apart of the modules.

United States Ratent [191 Block et a1.

[ Jan. 22, 1974 MEANS FOR SEALING MEMBRANE CARRYING TUBES [75]Inventors: Leo Block, Woodland Hills; Frank R. Shippey, Thousand Oaks,both of Calif.

[73] Assignee: Raypak, Inc., Westlake Village,

Calif.

22 Filed: Feb. 14, 1972 21 Appl. No.: 225,945

[52] US. Cl. 210/321, 210/433 [51] Int. Cl B01d 31/00 [58] Field ofSearch 210/321, 433, 497, 323

[56] References Cited UNITED STATES PATENTS 3,494,470 2/1970 Banfield210/32] Bush et a1. 210/497 X Lyall et a1 210/433 X PrimaryExaminerFrank A. Spear, Jr. Attorney, Agent, or Firm-Albert M. l-lerziget al.

[57] ABSTRACT An osmotic membrane bridges over the joint between an endcore fitting and the end of a tubular porous core member and alloys withthe material of the core fitting. The joints may be between modulesjoined or coupled by male and female plastic core fittings linkedtogether by bayonet joints. This assembly is adapted to use in reverseosmosis machines with the joined modules in a tubular shell forming anannulus with concentrate in the annulus under pressure. The bayonetjoints prevent pulling apart of the modules.

6 Claims, 8 Drawing Figures PATENTEI] JAN 2 2 I974 3,786,925 sum 1 or zPMENYED JAN 2 2 I974 SHEET 2 BF 2 MEANS FOR SEALING MEMBRANE CARRYINGTUBES SUMMARY OF THE INVENTION The invention relates primarily tosealing the ends of tubular members having a membrane on the surfacethereof. The invention is adaptable in many applications andenvironments. It has particular adaptability in desalination cells ofreverse osmosis machines, and the preferred form of the inventiondescribed herein is directed to adaptation in such a cell. The inventionis adapted in sealing where other fluids are involved such as in foodprocesses, etc. The cell might be called a reverse osmosis cell adaptedto be used with other fluids.

The invention in the preferred embodiment illustrated in the drawingsrelates to desalination cells adapted particularly for the desalinationor purification of water by means of an osmotic membrane element. Theillustrative embodiment of the invention is an improvement in the typeof cell shown more particularly in U.S. Pat. No. 3,400,825. This type ofcell embodies an elongated cyclindrical core made of porous materialwhich is positioned within a cylindrical housing providing an annularspace between the core and the housing. The osmotic membrane is on theoutside of the core member. The permeate finds its way through themembrane and the core to the bore within the core member, theconcentrate being in the annular space between the core and the housing.This is a very advantageous type of construction of a desalination cell,but in the industrial adaptation, fabrication, and utilization of suchcells, difficult problems have been encountered, solutions of whichconstitute objects of the herein invention.

One of the problems is the provision of an effective sea] at the end ofthe porous core member. The herein invention provides means in the formof core fittings joined to the ends of the porous core member with theosmotic membrane bridging the joint between the core member and the corefitting and alloyed with the core fitting to positively seal. Therealization of a sea] by this means is an object of the invention.

In commercial reverse osmosis machines, it is desirable to utilize alarge number of desalination cells in a compact assembly. In a preferredconfiguration, individual cells are positioned in straight lengths oftubing or in tube sections which form part of a continuous, serpentinechannel, there being a continuous flow of feed while the permeate istaken off from the cells by way of a manifold. Preferably, the cells areof modular construction comprising modules of predetermined lengths withmale and female end core fittings threaded to the core material. Themodules are joined by way of bayonet joints between the male and femalecore fittings. The core fitting at the end of a cell is closed by way ofa sealing plug. The membrane at the ends of the cell modules seals asdescribed in the foregoing. This construction provides an axially strongand rigid cell. The pressure of the water to be purified in the annularspace may run as high as 1,500 p.s.i. The pressure of the permeatewithin the cores may run as high as 40 to 50 p.s.i., depending on thehead to which the interiors maybe connected. When the pressure of thewater to be purified is shut off, the pressure within the cell isgreater than that in the annular space and the result is that the cell,which is mounted at one end will tend to pull apart axially. This hasbeen found to be a serious problem. An object of the invention is toovercome and solve this problem by way of the cell construction as justdescribed and to provide a simple but effective way of sealing the endsof the modules.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and additionaladvantages of the invention will become apparent from the followingdescription and annexed drawings wherein:

FIG. 1 is a cross sectional view of return bend sections of tubingconnected to a header for continuous series flow;

FIG. 2 is an exploded perspective view of one of the desalination cellsof the invention;

FIG. 3 is a cross sectional view of a single desalination cell of theinvention with the membrane in place within a feed tube section;

FIG. 4 is a detail view of a male end core fitting;

FIG. 5 is a detail view, partly in section, of a female end corefitting;

FIG. 6 is a cross sectional view taken along the line 66 of FIG. 5;

FIG. 7 is a detail sectional view of an end part of a core showing theseal provided by the membrane; and

FIG. 8 is a partial perspective view of the tube assembly of a reverseosmosis machine embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 of the drawings is asectional view of a part of the reverse osmosis machine as shown in FIG.8 showing a part of the tube sheet and header. The tube sheet isdesignated at 10 having secured in it the ends of the tubes 12 and 14which are sections of similar U-tubes 16 and 16'. Numeral l7 designatesa metal header casting which connects tube sections 12 and 14. Header 17has mounting lugs which can be attached to the tube sheet 10 by suitablemeans. It has two integral, cylindrical parts as indicated at 24 and 26which have extending bosses or nipples 28 and 30 having bores 32 and 34and counterbores 31 and 33 as may be seen in FIG. 1. These bores receivecylindrical parts of plastic fittings forming part of the desalinationcells as will be described more particularly presently. Within parts 24and 26 are bores 19 and 21 connected by passageway or port 23. Bores 19and 21 are beveled at their ends as shown and sealed to tube sheet 10 byO-rings 25 and 27.

The headers like 17 connect U-tubes like 16 in successive tiers atdifferent levels as may be seen in FIG. 8 which will be described morein detail presently.

Numeral 18 designates an inlet header casting and 18 designates asimilar casting which is an outlet header. Inlet header 18 is shown indetail in FIG. 3. It has a bore 29, counterbore 35, and counterbore 37.Bore 29 is beveled at its end and sealed to tube sheet 10 by O-ring 25.Header 18 has mounting lugs for attaching like casting 17.

Within tube 12 of U section 16 is shown a cylindrical desalination cell36 having plastic end fitting 38 which will be described more in detailpresently.

The desalination cell is shown in perspective in FIG. 2 and in crosssection in FIG. 3. The fitting 38 has a configuration as shown in FIGS.2 and 3. As may be observed, it has a cylindrical part 46 which hasequally angularly spaced ribs 48, the outside surfaces of which have ataper as shown at 50. The end part of each rib is cut away forming asquare shoulder as shown at 52. Numeral 54 designates one of a pair ofcircumferential bayonet slots near the end of fitting 38. Axial slot 56is one of a pair communicating with the circumferential slots. The endpart of the rib 48 has a radial slot as shown at 60.

At the left end of fitting 38 there are portions of progressivelysmaller diameter as designated at 62, 64, and 66. FIGS. 1 and 3illustrate the manner in which the fitting 38 fits into casting 18. Theend part 62 of fitting 38 is in counterbore 35 and abuts against anO-ring 70. Part 64 fits into bore 37. Part 66 extends exteriorly ofcasting 18. Fitting 38 has a cylindrical bore 72. Its right end extendsthrough tube sheet 10.

FIG. 1 shows core fitting 38' similarly assembled in header casting 17against O-ring 70.

Desalination cell 36 is formed in modular sections as may be seen inFIGS. 2 and 3. One of the sections comprises a cylindrical porous coremember which may be made of ceramic as designated at 76. The porousmember has a bore 78. Numeral 76' designates another similar modulesection. Section 76 has threaded end counterbores as designated at 80and 82. Numeral 86 designates a male plastic core fitting which is shownin detail in FIG. 4.

Fitting 38 in addition to the bore 72 has a first counterbore 90 and asecond counterbore 92. The male core fitting couples the porous section76 to end fitting 38.

Male core fitting 86 has a bore 96 of the same size as bores 72 and 78.It has an intermediate cylindrical part 100 having a diameter to fitinto the counterbore 92. It has an extending end part 102 of a diameterto fit into counterbore 90. It has an intermediate part 104 of a largerdiameter, this diameter being the same as the outside diameter of coremember 76. Core fitting 86 has extending threaded end part 106 which isof a size to thread into threaded bore 80 in the end of core member 76.The male core fitting 86 has extending projections or knobs 107 and 108.

FIG. 3 shows the assembly between the core member 76 and male corefitting 86 and end fitting 38. Threaded end 106 of core fitting 86 isthreaded into threaded counterbore 80 in the end of core member 76 withpart 104 abutting against the end of the core memher. The male coremember 86 is joined to the end fitting 38, the extending projections 107and 108 having been received into the axial slots 56 and 56' in the endof fitting 38 after which these projections are rotated into thecircumferential slots 54 and 54' in fitting 38, thus, forming a bayonetjoint or lock between these parts. Part 100 fits against O-ring 101 inbore 92.

Numeral 120 designates a female core fitting at the other end of coremember 76. It is shown in detail in FIG. 5. lt is cylindrical, having anoutside diameter the same as the outside diameter of the core member 76.It has an extended threaded part 122 of a size to thread into thethreaded counterbore 82 in the end of core member 76. it has a bore 124of the same size as bores 72, 78, and 96. It has a first counterbore 126and a second counterbore 128. It has axial slots 130 and 130' andcircumferential slots 132 and 132' adapted to form part of a bayonetjoint or coupling. Numeral 86 designates a second male core fittingwhich in FIG. 3 is assembled to the female core fitting 120 in themanner already described in connection with fitting 38. Between part ofcore fitting 86' and the bottom of counterbore 128 is provided a sealingO-ring 136.

Numeral 76' designates another modular core section to the right end ofwhich is joined another female core fitting which is like the corefitting 120. Numeral 140 designates an end plug which may be made ofplastic and which serves to close the end of the desalination cell. Ithas a cylindrical body 142 of a diameter to fit into the counterbore128' in core fitting 120. The body has an end flange 144 as shown. Atthe other end is a tapered extension or plug 146 adapted to extend intobore 78 in core member 120' to close it. End member 140 does not haveextending projections adapted to be received in axial slots a and 1300'in core fitting 120' and to be turned into the circumferential slots132a and 132a, although it could have. Pressure in the U-tube holds endplug in position.

Numeral 158 designates the membrane which is on the exterior of the coreof the desalination cell. Typically, the membrane consists of an outerskin and a jelly-like substructure which is between the skin and theouter surface of the core, as illustrated in FIG. 7. The membrane may beof various types, for example, it may be of a type referred to in (1.8.Pat. No. 3,400,825 or of other types known in the art. The problem whichhas been encountered in this type of construction in the past has beenof sealing the membrane to the pressure vessel which surrounds orencloses the desalination cell. In the construction shown and asillustrated in FIG. 7, porous core member 76 is closed by male corefitting 86 which has the threaded part 106 threaded into threaded bore80. This seals the end of the bore and also provides axial strength andrigidity. It is possible to adhesively attach the core fitting, but thestructure shown is preferred. As may be seen in FIG. 7, membrane 158,which is applied to and on the desalination cell, bridges the jointbetween core fitting 86 and the end of core member 76. Membrane 158 isterminated at part 100 of core fitting 86 as shown in FIG. 7. Also,preferably, the material of core fitting 86 is selected so that isunites chemically with membrane material 158 to form an alloy of the twomaterials so as to positively insure a perfect seal. The membranematerial may be cellulose acetate composition as shown in the art andthe core fitting material may be a polycarbonate plastic, by way ofexample.

The direction of flow, that is the feed fluid and permeate in FIG. 3, isindicated by the arrows.

As explained, there are a plurality of U-tubes like the tubes 16connected to headers 17 mounted from tube sheet 10 with a desalinationcell in each tube section with a continuous series flow of feed fluidthrough the tubes as illustrated in FIGS. 3 and 8.

The end parts 66 of fittings 38 which extend from the headers connect toa permeate manifold as may be seen in FIG. 8. Manifold 170 has fourseries of equally angularly spaced nipples as indicated at 172, theseseries of nipples being connected to the end parts or nipples 66 of thedesalination cells. The purified water is drawn off through thismanifold. The feed of water to be purified or desalinized connects tothe inlet header 18 as designated by the arrow. Feed is admitted asshown by the arrow at header 18 and travels through two banks of tubes,each having an inlet header 18. The outlet is from outlet header 18'from the lower bank.

In FlG. 2, there is shown a slightly modified form of header asdesignated at 172. This header corresponds to header 17. This header hasan intermediate tubular part 174 and end sections 176 and 176' havingfaces 177 and 177 which attach against tube sheet 10. These faces havecylindrical bosses 178 and 178' with extending tubular nipples 180 and180' through which the end parts 66 and 66 of end fittings 38 extend.Numerals 182 and 182 designate holes for securing bolts insertablebetween webs 183, 184, 183' and 184'.

If desired, headers like 17 and 18 can be fabricated as an integralheader unit rather than being two separate parts.

From the foregoing, those skilled in the art will fully understand thenature and construction of the invention, its operation, and the mannerin which it acheives and realizes the objects and advantages set forthin the foregoing.

The foregoing disclosure is representative of a preferred form of theinvention and is to be interpreted in an illustrative rather than alimiting sense, the invention to be accorded the full scope of theclaims appended hereto.

What is claimed is:

l. A filter element comprising;

a porous core member having a cylindrical exterior surface and a boretherethrough having a cylindrical surface; a connector fitting ofmaterial other than that of said core member secured to an end thereofand having inner and outer cylindrical surfaces constituting axialcontinuations of said exterior surface and the surface of said bore; anda permeable membrane covering one of said surfaces of said core member,extending across the joint between said core member and fitting andbeing sealingly secured to said fitting.

2. A filter element as in claim 1, wherein said membrane is on theoutside of said core member and bridges the outside of the joint betweenthe core and said fitting.

3. A filter element as in claim 2, wherein the membrane material and thefitting material are constructed of materials such that they unitechemically to form an alloy of the two materials.

4. A filter element as in claim 1, wherein said fitting has threadedengagement with the core member.

5. A filter element as defined in claim 1 wherein said fitting isconfigurated to constitute the one part of a coupling having male andfemale parts, said core member having a fitting at the opposite endconfigurated to constitute one part of a coupling having male and femaleparts, said male and female parts being constructed to provide a bayonetjoint for holding them together against axial pressure and in sealingrelationship, whereby a plurality of core members and fittings can beassembled into a continuous elongated unit.

6. A system embodying a plurality of relatively short porous memberseach having an exterior cylindrical surface and having an axial borepresenting a cylindrical surface; a semipermeable membrane covering oneof said surfaces; a plurality of fittings of material other than that ofthe core members secured to the ends of core members; and means wherebythe ends of fittings are securable together to form separable sealedjoints, whereby a relatively long assembly can be formed of relativelyshort porous core members and fittings detachably secured together inaxial alignment, said semipermeable membrane bridging the joints betweenthe ends of core members and their corresponding fittings and beingsealingly secured to said fittings.

1. A filter element comprising; a porous core member having acylindrical exterior surface and a bore therethrough having acylindrical surface; a connector fitting of material other than that ofsaid core member secured to an end thereof and having inner and outercylindrical surfaces constituting axial continuations of said exteriorsurface and the surface of said bore; and a permeable membrane coveringone of said surfaces of said core member, extending across the jointbetween said core member and fitting and being sealingly secured to saidfitting.
 2. A filter element as in claim 1, wherein said membrane is onthe outside of said core member and bridges the outside of the jointbetween the core and said fitting.
 3. A filter element as in claim 2,wherein the membrane material and the fitting material are constructedof materials such that they unite chemically to form an alloy of the twomaterials.
 4. A filter element as in claim 1, wherein said fitting hasthreaded engagement with the core member.
 5. A filter element as definedin claim 1 wherein said fitting is configurated to constitute the onepart of a coupling having male and female parts, said core member havinga fitting at the opposite end configurated to constitute one part of acoupling having male and female parts, said male and female parts beingconstructed to provide a bayonet joint for holding them together againstaxial pressure and in sealing relationship, whereby a plurality of coremembers and fittings can be assembled into a continuous elongated unit.6. A system embodying a plurality of relatively short porous memberseach having an exterior cylindrical surface and having an axial borepresenting a cylindrical surface; a semipermeable membrane covering oneof said surfaces; a plurality of fittings of material other than that ofthe core members secured to the ends of core members; and means wherebythe ends of fittings are securable together to form separable sealedjoints, whereby a relatively long assembly can be formed of relativelyshort porous core members and fittings detachably secured together inaxial alignment, said semipermeable membrane bridging the joints betweenthe ends of core members and their corresponding fittings and beingsealingly secured to said fittings.